Technology industry heavyweights have been dragged further into the US snooping scandal after it emerged that many, including Microsoft and Intel, work hand in glove with security agencies, providing them with sensitive information in exchange for classified intelligence.

News agency Bloomberg cited four unnamed sources who claim that makers of hardware, software, communications equipment and security tools work with US security agencies not only to protect national interests, but also to attack rivals' computer systems.

According to the report, Microsoft provides US officials with early warnings about vulnerabilities in its software, enabling them to exploit weaknesses in targets' systems.

Elsewhere, Intel's McAfee unit is alleged to be so close to the FBI, CIA and National Security Agency that its president is regularly approached by the security services to clear specific company employees to work with investigators.

While it has long been understood that technology companies would work closely with governments in order to safeguard national security, the revelation that firms help security services to launch attacks on others will likely prove inflammatory.

Tensions around the relationship between the tech industry and government were heightened after a former NSA contractor, Edward Snowden, leaked top-secret documents detailing the information-sharing arrangements between the NSA and firms such as Google, Microsoft, Apple and Facebook.

Snowden has subsequently accused US security services of attacking scores of targets based in China. For their part, Google, Microsoft, Apple and Facebook had all denied knowledge of the so-called PRISM system.

Neither Microsoft nor McAfee had responded to request for comment on the latest revelations at the time of publication.